Thursday, January 28, 2016

Front Wheel Alignment

Front Wheel Alignment for A Tri Five Classic Chevy After a Disc Brake Upgrade 1955, 1956, 1957 Chevrolet

   -Alan Arnell

I have been told that once I install my new Chevy disc brake parts on my 1957 Chevy that the car at low speeds will more than likely drive and turn okay.  However, I may develope a problem from the retrofit installation when driving at interstate speeds.  The common problem is that the upgraded disc brakes might make the car not want to stay in a straight line going dead ahead.  

This problem is common to the disc brake upgrade.  The main culprit is the fact that the front wheels after the installed disks will extend outward from ¾ to 1 inch from the track the drum brakes produced on each side.  The extension of the wheels away from the original turning axis will increases the distance from the turning axis.  This increases the up and down movement of the wheel and tire during turns.  

The common fix for this problem is that 2-½ to 3 ½ degrees of positive caster must be dialled in to the front suspension.   This measurement is also recommended whenever a Classic Tri Five Chevy has any late model improvements, such and disc brakes and power steering improvements.  

The movement of the upper ball joints to the rear (Positive Caster) slows the steering down and gets rid to the overly sensitive feel.  An additional extra ¼ to ½ degree may be added to the right side to compensate for the crown in the road.  

Recommended Adjustments
Caster Camber Toe In
Stock Steering Box +½ to 1 degree 0 to -1 degree ⅛” to 3/16”
605 Pwr Steering +2 ½ to 3 ½ degree 0 degrees driver ⅛” to 3/16
Box or Rack & side & -¼ passe-
Pinion Unit enger side

It is more than likely easier to take your car to an established alignment shop that understands Tri Five Chevys.  Many place don’t, so ask around.   But if you want to be a do it yourself kinda guy here are some instructions.

There are three separate adjustments to getting a proper front end alignment.  To properly position the front alignment the Camber, Caster and Toe must be set.  

Camber is when you face the front of your car then look at the front tires.  If the tips of the tires are tilted inward they have negative camber.  If the tires are tilted outward they have positive camber.
Camber will help tire-wear or destroy tires if not set correctly. Handling of the car is also determined by having the correct camber.  On the other hand, camber has little or no effect on straight-line driving.

Caster is the measurement of whether the top of the tire is adjusted forward or to the rear of the car from a side view.  Think of a peace sign,  The top line hits the top of the peace sign at zero.  If the top center is angled rearward the caster is positive.  Forward and it is negative caster.  Positive caster creates high-speed stability and turns the steering wheel during a turn back to center.  This is because a part of the vehicle weight is behind the tire.  That weight helps position the tire straight ahead.  Negative caster is where the top center is tilted forward past vertical.  Negative caster will reduce steering effort. That happens because the weight moves forward of center.  However, negative caster is not good for freeway speeds.

Toe is the amount the front tires are turned inward, like if you angle your feet in while standing.  Toe-in is where the tire is turned inward. Toe-out is when the leading edges of the front tires are angled outward as viewed from above.   Both in and out helps or hinders tire wear.  The usual spec is for a slight toe-in to compensate for normal pressure that forces tires outward as the car goes down the road.

To complete your own front wheel alignment one could use digital angle finders.  But, using this tool requires math.  So, forget that!   An easier way uses a basic bubble gauge.  Though not necessary, a turn plate will help by allowing you to perform the 20-degree turn-in and turn-out measurements of caster.  The plate are also good for toe adjustments.  With the bubble gauge attached to the wheel and leveled it will read out camber.  To change camber the upper control arm must be changed by inserting or removing shims.

Caster is the next angle to set.  Turn the tires in 20 degrees. Zero the caster reading on the gauge. Next turn the wheels 20 degrees out and the gauge will read the amount of positive or negative caster.  Positive caster is put in by either adding shims to the rear bolt or removing shims from the
front attachment point for the upper control arm. This adjustment will affect the camber, so you will have to check and set it again.

Now adjust the toe. Note: when adjusting the toe you must push the car backwards and forward about 10 feet.  Doing so will load the front tires to make for the best readings.  Toe is always set last because adjusting the camber and/or caster moves the control arms, which changes the toe. Usually the tie rods have left and right hand threads with a threaded sleeve and locking nuts to prevent the adjustment from changing.  It is best to move the left and right side adjusters the same amount until you get the correct toe-in.

Links to more Power Brake Posts:

Tri-Five Late Model Power Booster Conversion Part 1

Power Booster Conversion Tri-Five Late Model Part 2
Power to the Front
Move to a Dual Purpose MC and Disk Brakes
Front Disc Brakes for a Tri-Five Classic Chevy

Power Booster Conversion Tri-Five Late Model Part 3
Tri-Five Classic Chevy
Proportioning Valve, Dual Master Cylinder and Brake Lines

Brake Pedal Clevis Relocation After A Power Assisted Disc Brake Upgrade on a Tri Five Chevy.

Front Wheel Alignment

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